Triangular Juxtaposition Diagrams: Incorporating Across-Fault Growth to Reduce Uncertainty

Abstract

Abstract

Triangular juxtaposition diagrams are commonly used to quickly evaluate across-fault hydrocarbon sealing capacity in the absence of a complete 3D model. The diagrams are constructed by linearly displacing a layer-cake model across a hypothetical, vertical fault. The resulting triangular juxtaposition plot is composed of horizontal footwall horizons and diagonal hanging wall horizons, where displacement increases along the x-axis and depth increases down the y-axis. Traditionally the stratigraphy used to construct the diagrams has been derived from a single well, and, therefore does not incorporate across-fault sedimentary growth. This assumption can negatively impact the accuracy of the modelled juxtapositions and fault sealing capacity by failing to incorporate the true stratigraphic thicknesses in the fault footwall and hanging wall. Constraints on the magnitude of cross-fault sedimentary growth is, however, often readily available from secondary wells or adjacent seismic reflection data. Using these data, two new types of juxtaposition triangle diagrams: “Two-Well” and “% Growth” triangle diagrams, can be constructed.

Defining growth data either from a secondary well or as a percentage increase in across-fault thickening, the new techniques presented here are used to model lithological juxtapositions and quantitative fault seal proxies (including shale gouge ratio, clay smear potential and shale smear factor) on a series of synthetic and real world examples. The results indicate that Two-Well and % Growth diagrams, which are integrated into Midland Valley's Move software suite, provide a more accurate representation of the fault than the traditional 1D solution, with no impact on speed or ease-of-use. Incorporating these techniques into the early stages of a fault seal study can provide higher degree of certainty in the capacity for a fault to act as a migration pathway or barrier to cross-fault flow, reducing cost and uncertainty at an early stage of exploration.

AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016